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Safe maximum side bending temperature?
https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=46756		 Page 1 of 1
Author:  Colin North [ Tue Dec 01, 2015 3:46 am ]
Post subject:  Safe maximum side bending temperature?
Bending a 0.075" thick Ceylon satinwood (chloroxylon swietenia)? side and got a fair bit of springback.
Using SSII, very little water and a bending machine with blanket, temp was taken up quickly to 300/310 F for 15 minutes, then cooled for 1 1/2 hrs before temp taken up again to same 300/310 F for 5 minutes. Then left overnight to cool.
I think the temperature may have been a little low?
Anyone got any suggestions for a (safe) temperature limit for side bending with a non-oily wood? It's a light coloured wood and don't want to scorch it!
Author:  Michaeldc [ Tue Dec 01, 2015 7:59 am ]
Post subject:  Re: Safe maximum side bending temperature?
340°F is my current max using parchment/masking paper on both sides. I then cook for 20 minutes at 280°F for twenty minutes and allow it to return to room temperature. For wood known for spring back, I repeat the last operation at least 3 times. Works for me..

M
Author:  bluescreek [ Tue Dec 01, 2015 8:52 am ]
Post subject:  Re: Safe maximum side bending temperature?
you can go to 375 hold for about 2 min then let the temp set at 250F for about 15 min. Once cool ( about 40 min ) you can take out and clamp to mold.
Author:  Colin North [ Wed Dec 02, 2015 8:14 am ]
Post subject:  Re: Safe maximum side bending temperature?
bluescreek wrote:
you can go to 375 hold for about 2 min then let the temp set at 250F for about 15 min. Once cool ( about 40 min ) you can take out and clamp to mold.

375 - wow7-eyes
I take it that this won't darken the side significantly, even with light colored wood, with only 2 minutes at that temperature, just seems really hot.
I see you offered the same advice for the post about Bubinga, so it's not likely to be a typo.
Would this be a good method for maple, and do you use supersoft, or just this temperature works.?
Author:  Alan Carruth [ Thu Dec 03, 2015 2:14 pm ]
Post subject:  Re: Safe maximum side bending temperature?
The safe bending temperature will depend on when the lignin starts to discolor, and will vary with the species and sample. Test if you can.
Author:  kencierp [ Thu Dec 03, 2015 2:51 pm ]
Post subject:  Re: Safe maximum side bending temperature?
We have side profile templates for all our models so I can mark the inner most waist curve and use that as our positioning aide throughout the construction process. An added benefit is that if need be, we have the cut off section of the side that can be used for test bending to establish heat and moisture requirements for each set of sides.
Author:  Colin North [ Tue Dec 08, 2015 2:50 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Just for information, 375F, hold for about 2 min then let the temp set at 250F for about 15 min is ace for curing springback, but turns the Ceylon Satinwood (chloroxylon swietenia) from a golden shiny glow to a nice shade of Tan.
No panic, just a test on offcuts.
Back to the "drawing board".
Author:  Grant Goltz [ Tue Dec 08, 2015 3:51 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Colin North wrote:
Just for information, 375F, hold for about 2 min then let the temp set at 250F for about 15 min is ace for curing springback, but turns the Ceylon Satinwood (chloroxylon swietenia) from a golden shiny glow to a nice shade of Tan.
No panic, just a test on offcuts.
Back to the "drawing board".

Well, that is not surprising since that is the temperature (190C) that thermally modified wood is heated to. So just keep it there for an hour and it will be toasted all the way through, nice and brown :lol:

Actually 2 minutes should not really penetrate much and should sand off. Biggest problem is that no method of heating during bending is perfectly uniform, so you are bound to get more "toasted" spots.

Grant
Author:  Colin North [ Tue Dec 08, 2015 4:33 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Tried sanding off, no go!
But it is reasonably even....
Author:  Rod True [ Tue Dec 08, 2015 4:44 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Some woods require more initial moisture during the heating/bending process to keep their shape once bent.

So with the off cuts how did the higher temperature do as far as holding the shape goes? Don't think you mentioned that, just that you got some "roasting".
Author:  Colin North [ Tue Dec 08, 2015 4:57 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Rod True wrote:
Some woods require more initial moisture during the heating/bending process to keep their shape once bent.

So with the off cuts how did the higher temperature do as far as holding the shape goes? Don't think you mentioned that, just that you got some "roasting".

By "ace for curing springback" I meant there was virtually none at all.
I am using SSII because of the interlocking grain, but was avoiding more water (just a quick wipe with a wrung out damp cloth) because the sides were rift to flat sawn, and the last set I built with cupped quite badly due to too much of the damp stuff.
I have another set which is pretty much perfectly quarter sawn, and I can probably use more moisture with that one.
Thanks for the tip Rod.
Author:  Colin North [ Thu Dec 10, 2015 3:55 am ]
Post subject:  Re: Safe maximum side bending temperature?
You don't always get to see the results of requests for advice, so...

Did some more testing with offcuts, and decided after Rod's reminder to go with a new set, sides properly quarter sawn.

Attachment:
DSCN3273.JPG


Tested the side offcuts from that.
SSII overnight, dry off, spray down, rub in, wipe off (basically more water)
Blanket on top, light bulbs underneath.
310/320 for 5 mins, down to 260/270 for 15 mins.
Cool off (2 hrs)
"Shock" quickly to 310/320, immediately back to 260/270 for 15 mins.
Cool overnight, straight to the mold, job done.

Thanks Rod, I got a bit blinkered after my previous cupping problems with the Ebay set.

Attachment:
DSCN3276.JPG
Author:  Joe Beaver [ Sat Dec 12, 2015 12:56 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Colin, great looking bend. You did nail it!!!
Author:  Pmaj7 [ Sat Dec 12, 2015 3:58 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Collin, I like the connectors on your mold. Simple, very solid looking and unobstructed area for clamping! (Or should I say mould? I know ya'll invented the language!)
Author:  Colin North [ Sat Dec 12, 2015 6:43 pm ]
Post subject:  Re: Safe maximum side bending temperature?
Shhhh!............
You'll give all my secrets away! gaah
laughing6-hehe
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